Whether it can be used to develop a true third party, I can’t say. However, can it build support for and awareness of centrist beliefs and policies — absolutely. In fact, that is already happening in social media.

I just did a quick search of blogs about centrist or moderate parties on Technorati and you will be delighted I think with what is available right now. For example, have you checked out the following, which you can learn more about on the U.S. Politics Guide blog. (http://uspoliticsguide.com/American_Political_Directory/Centrist_Political_Blogs.php

Centrist Blogs
TheCenterLane.com – No cult. No mission.
News, commentary and opinion from the middle of the road.

Right Democrat – Speaking for the moderate & conservative Democrats. Right Democrat is the voice of Democrats who believe in economic populism and social traditionalism.

Andrew Sullivan – Writer in the Atlantic Magazine. He has worked as a contributing writer and columnist for the New York Times Magazine, a regular contributor to the New York Times Book Review, and a weekly columnist for the Sunday Times of London. Sullivan has been a columnist for Time Magazine, and a regular guest on HBO’s “Real Time with Bill Maher” and NBC’s “Chris Matthews’ Show.”
We Stand Divided – Promotes the benefits of divided government. “It is not enough that your Legislature should be numerous; it should also be divided.” Ben Franklin “Ambition must be made to counteract ambition.” James Madison “Divided we ever have been, and ever must be.” John Adams “Divided we stand, united we fall.” Thomas Jefferson.
Moderate Voters – If you’re tired of the Far Right and the Far Left this is the blog for you. News, analysis, commentary and political opinion.
The Independent Voter – Opinions about moderate politicians and candidates. Timely writing covering both sides of the political table without going to the extremes.
Centerfield – Centerfield is the blog of the Centrist Coalition. Political talk and opinion form the middle.

American Moderate Party – Political blog coming from just right of center. Attempts to bring Republicans back to the party of Lincoln.
The Moderate Voice – Domestic and international news, analysis, irrevent comments, original reporting, and popular culture features from across the spectrum blog from Santa Monica, California. Discusses current news, events& presidential politics. Many Centrist & Progressive Blog links.
Donklephant – As the name dictates. Political opinion from both sides of the aisle focusing on moderate opinions.
American Centrist – Centrist blog with timely news & opinions discussing a variety of political topics.
The Centrist – A Pennsylvanian’s moderate conservative commentary about state and national politics.
Centerfeud – Thoughts & opinion from the Left & the Right. Includes blog feeds & Issue-oriented essays.

Judy, you’ll probably have your hands full just looking at all these blogs and then reviewing their blogrolls. You may want to choose the ones you want to subscribe to (are you familiar with this — you can use Google Reader, for example, so that you can read all the new posts for your favorite blogs. It will save you lots of time.

Also, if you read what social media groups the bloggers you like best belong to, you may want to sign-up on their community — that way you can really get to know the online community that shares your interests. Beyond that, just do what you did here (for which I am very appreciative!) Comment on blogs that you like the best and soon you’ll see how social media today is already making a dent in promoting moderate political positions. And to the extent that we are somewhat stuck with the parties that we have, you may want to build an online relationship with bloggers supporting the Democrats or the Republicans — to the extent that we are stuck with the 2-party system, I think it pays to try to help them appreciate the need for centrist positions and stop letting the fringe in each party dominate.

Lengthy answer, but I hope it helps. Would love to hear more on your efforts.